Why are we ticklish?
人怕挠痒痒的原因
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Professor Sukhi Shergill, Psychiatry and Systems Neuroscience, King's College London
苏基·谢吉尔 伦敦大学国王学院精神病学与系统神经科学教授
Tickling: love it, or hate it? Or even a bit of both... It's a strange phenomenon.
“被人挠痒痒这种感觉：你是喜欢还是讨厌?或者都有一点… 这是个奇怪的现象。”
There are two types of tickling sensation. Knismesis - a mildly annoying feeling caused by light movement like this. And there's gargalesis- which is caused by a deeper pressure on your skin.
痒的感觉分为两种：“触觉痒”指由这种轻抚的动作引起的轻微不适感;“逗笑痒”是通过给皮肤施加更强的力道而引发的。
When your skin is touched, the nerve endings underneath send electrical signals to the brain. We laugh when we're tickled because the sensation is picked up in two areas of the brain at once - the part which analyses touch, but also the part that creates pleasure.
当你的皮肤被触碰时，皮下的神经末梢会向大脑传送电子信号。我们被人挠痒痒之后会发笑，因为这种感觉会同时出现在大脑的两个区域中：分析触觉的区域，以及产生愉悦感的区域。
But of course, being tickled isn't always enjoyable.
当然，被挠痒痒并不总是件令人感到愉快的事情。
In fact, it also affects the part of the brain that makes you feel panic in the face of danger.
事实上，它还会影响大脑中使你临危恐慌的部分。
So, strange as it may seem, laughing when you're tickled could be a sort of primitive defence mechanism - giving a signal to show our submission to a predator.
所以，虽然看起来很奇怪，但被胳肢后大笑可能是一种原始的防御机制，就好比是身体通过发送信号来展现对捕食者的顺从。
So, why can't we tickle ourselves? We think it's to do with the brain's cerebellum that monitors our movement. It can tell the difference between expected and unexpected sensations. In other words, it already knows what you're doing and is too clever to react.
那么，为什么不能胳肢自己呢?我们认为这和小脑有关，小脑负责监控身体的运动。它能区分预期和意外的感觉之间有何不同。换言之，它已经知道你在做什么，只是因为太聪明而不作出反应。
词 汇
tickling sensation
痒的感觉，发痒
nerve endings
神经末梢
electrical signals
电子信号
defence mechanism
防御机制、防卫表现
